From what I understand, picture books tend to pay lower advances and I think royalties (not sure about that one though) which is why agents don't usualy rep them. Novels typically pay more on both sides. YA typically pays less than adult fiction, though YA has been profitable recently since it's been a hot topic for a few years. I've been hearing that this is on the downslope now. I suspect another genre/market will become hot and they'll get all the money for a while.
Any advance is based on how good the book is, how much the publisher thinks they'll make off the book, and what the budget is. It varries wildly. There have been picture books that earned a bigger advance than novels, and vice versa. First-time author doesn't really play that much into it. I was a first-time author and I got a six-figure advance.
You have the same odds of getting published no matter what you publish. If the book is good, your odds are high, if not, your odds are low. With picture books, you can approach publishers directly, where with novels, you're better off (IMHO) having an agent first. Agents will get you bigger advances, and they know all the publishing stuff you don't.
Don't write what you think will make you the most money. Write what you feel passionate about. If you love PBs, then do them. If you love YA, do that. Do both if you love them equally. But don't write for a market just because you read it's hot and easy to get published there. If you don't know the market and genre, the chances of you understanding what makes a good book in that genre are slim.